1. Field of the Invention
This invention relates to a vapor phase process for the production of gamma-butyrolactone, and, more particularly, to a method and apparatus for forming a vapor mixture of a feed compound and hydrogen in such process.
2. Description of the Prior Art
Gamma-butyrolactone is a stable, well-known compound that is a liquid at -44.degree. C. to 204.degree. C. It is used as an intermediate in the manufacture of 2-pyrrolidone, alpha-tetralone and glutaric acid; in the solvent welding of plastic films; as a swelling agent for cellulose acetate films; and as a non-corrosive solvent for polymers in general, acetylene and water-immiscible alcohols.
In general, the catalytic hydrogenation of maleic anhydride and/or other related compounds to produce gamma-butyrolactone (hereinafter referred to as "butyrolactone") is an old and well established art for which a great many processes have been used, the most important of which historically have been effected in the liquid phase.
An alternative to the commercially-used, liquid phase catalytic hydrogenation of maleic anhydride, succinic anhydride, etc. feedstocks is vapor phase hydrogenation, at low pressures, in the presence of a generally different class or type of catalyst. Exemplary of patents covering vapor phase catalytic hydrogenation of conventional feedstocks to butyrolactone include, for example, U.S. Pat. No. 3,065,243, wherein the conversion to butyrolactone is effected at low pressures in the presence of a copper chromite catalyst.
De Thomas, in U.S. Pat. No. 4,105,674, also described a vapor phase process in which the feed reactant mixture was formed by passing hydrogen through maleic anhydride in a vaporizer maintained at a temperature of 130.degree. -190.degree. C. However, in this method, the rate of vaporization of liquid maleic anhydride did not provide a suitable flow rate of reactant for commercial production of butyrolactone. Furthermore, maleic anhydride reacts with recycle components at these temperatures.
Attig, in EPA 332,140, published Jun. 28, 1989, described a vapor phase, catalytic hydrogenation of maleic anhydride to tetrahydofuran and butyrolactone. In this process, the vapor mixture of maleic anhydride and hydrogen was formed by pumping molten maleic anhydride into a stream of hydrogen in a vaporizer at 155.degree. C. However, the rate of vaporization of maleic anhydride was limited by the slow transfer of heat from hydrogen gas to the mass of molten maleic anhydride.
Other pertinent references in this field include U.S. Pat. Nos. 3,580,930; 3,894,054; 4,032,458; 3,853,922; 3,948,805; 4,001,282; 4,006,165; 4,032,458; 4,048,196; 4,083,809; 4,105,674; 4,810,807; and U.K. patent Nos. 1,168,220 and 1,293,151.
Commercial practice in respect of the production of butyrolactone from a vapor mixture of maleic anhydride and hydrogen by catalytic hydrogenation has not been entirely successful, not only because of the short lifetime afforded by conventional hydrogenation catalysts, but also because of the low rate of vaporization of molten maleic anhydride into a hydrogen stream, particularly a hot, reactive recycle hydrogen stream.
It is also well known that heating to elevated temperatures, e.g. above 135.degree. C. can cause rapid decomposition/charring of maleic anhydride.
Accordingly, it is an object of this invention to provide an improved vapor process for the production of butyrolactone from a vapor mixture of a feed compound such as maleic anhydride and hydrogen.
Another object of the present invention is to provide a process for forming a high flow rate of feed compound in recycle hydrogen gas.
Still another object herein is to provide a continuous vapor process including a vaporizer apparatus in which a liquid feed compound is converted into finely divided droplets which can be vaporized rapidly in hot, recycle hydrogen gas.
Another object is to vaporize maleic anhydride in an extremely short time at elevated temperatures and before decomposition can take place.
Yet another object is to provide a vaporization process in which there is a relatively low pressure drop between the recycle hydrogen gas entering and leaving the vaporizer as compared to other vaporization processes known in the art.
These and other objects and features of the invention will be made apparent from the following more particular description of the invention.